1. Field of the invention
The invention relates to a process for heating solid materials containing volatile matters, and more particularly to a process and an apparatus for performing the process of the type, in which a conveyor is used for transporting solid materials.
2. Description of the prior art
An externally-heating type rotary kiln has been often used for drying materials. In this respect, in case moisture is desired to be removed and vapor produced by heating is relatively light in weight, it has been a general practice to use a substituting gas of a light weight such as nitrogen gas for purging the vapor thus produced. This appears to pose no problem hitherto. However, in case carbon is derived by thermally decomposing waste tires, waste rubbers and the like, since heavy oils of a large molecular weight have been adsorbed thereto, the vapor and a substituting gas such as nitrogen gas are separated into two layers/ because of a large difference in specific weight between the gas and the vapor, with the result being that a substituting gas only passes above an oil-vapor layer, thus failing to thereby substitute the latter. One of solutions to this problem may be to provide means, in which an exit for gas is positioned on the opposite side of an exit for dried solid materials, for instance, carbon, i.e., on the side of an entrance of a kiln, such that gas counterflows the feeding direction of carbon. However, this provision still fails to avoid a shortcoming in that, due to the characteristic of a rotary kiln, the position of an exit for carbon is lower than an entrance, so that part of oil vapor flows towards the carbon exit, and is condensed in a low temperature portion, and again stuck to carbon again. Thus, the desired drying effect can not be achieved. If an injection rate of a substituting gas is increased excessively, as compared with a rate of oil vapor being produced, there is created turbulence within a rotary kiln, thereby enhancing a gas-substituting effect. However, the turbulence thus created blows carbon powder upwards to carry the same way. For this reason, an increase in injection rate of gas is not preferable.
In a continuous operation of a rotary kiln or a fluidized bed furnace, gas and oil vapor are produced due to decomposition of rubber, and part of the oil vapor is condensed in a low temperature portion to be stuck to carbon, thereby increasing the amount of a volatile matters and odor and thus exerting an adverse effect on the quality of products. In principle, oil which is stuck to carbon may be removed by heating carbon to a temperature above a boiling point of oils to vaporize the oils, and then substituting oil vapor by a dried gas such as an inert gas. However, difficulties arise in removing oils completely for the following reasons.
Oils stuck to carbon provide an average molecular weight of about 200 at a thermally decomposing temperature on the order of 600.degree. C., so that even if oils are vaporized, the specific weight of oil vapor is considerably high. In contrast thereto, nitrogen gas used as a substituting gas is light in weight, resulting in insufficient substitution, and oil vapor tends to be condensed again, thereby adhering to carbon.